1. Field of the Invention
The present invention relates generally to a multiple drop per spot printing system with multiple printheads, and more particularly, to a method for reducing simultaneous drop ejections from the multiple printheads to reduce peak power consumption of the printing system.
2. Description of Related Art
Ejectors of multiple drop per spot printing systems are known to be able form a spot of ink on a recording medium with multiple drops of ink over a spot (or burst) cycle. More specifically in multiple drop per spot printing systems, each spot of ink is formed on a recording medium over a spot cycle using one or more drops of ink, up to a maximum number of N drops of ink. Examples of multiple drop per spot printing systems include thermal ink jet (TIJ), piezo-electric, and acoustic ink printing (AIP) systems.
Some multiple drop per spot printing systems are configured with two or more printheads. For example, color printing systems have four printheads for individually ejecting one of the colors cyan, magenta, yellow, and black. The printheads of these multiple drop per spot printing systems can be either partial array or full width array printheads. Full width array printheads span an entire page, whereas partial width array printheads span a fraction of a page. Full width array printheads move in a fast scan process direction, whereas partial width array printheads move in a slow scan and a fast scan process direction to achieve full page coverage.
In addition, some multiple drop per spot printing systems that are configured with multiple printheads have a single power supply. The single power supply is used to simultaneously actuate the multiple printheads to fire droplets of ink. Ideally, the single power supply has sufficient power to simultaneously drive all of the ejectors of all of the printheads at one time, thereby achieving 100% coverage on a recording medium. Generally, the peak power demands of a power supply driving multiple printheads during any spot cycle, however, is some level of power that produces less than 100% coverage. In order not to have a power supply with excess capacity, most printing systems assume that the spot cycles of multiple printheads will not require more than some predetermined peak power rate.
Generally, the power supplies for driving multiple printheads is an expensive component of multi spot per drop printing systems, and in particular for acoustic ink printing systems. To minimize the per unit costs of such printing systems, it would be desirable to provide a multiple drop per spot printing system in which the predetermined peak power consumption required for operation is minimized. By minimizing peak power consumption, the power required during any one actuation interval of the printing system""s multiple printheads is advantageously reduced.
In accordance with the invention there is provided a multiple drop per spot printing system and method of operation therefor. The multiple drop per spot printing system includes at least a first printhead and a second printhead that move in a process direction. The two printheads have ejectors for ejecting onto a recording medium drops of ink. Each printhead ejects up to N drops of ink onto the recording medium to form a spot of ink during a spot cycle. A memory is coupled to the first printhead and the second printhead for specifying which ones of the ejectors to actuate during the spot cycles of each printhead. Also, a power supply is coupled to the first printhead and second printhead for simultaneously actuating the ones of the ejectors specified by the memory during the spot cycles of each printhead. The first printhead is offset in the process direction from the second printhead a non-multiple number of N drop separations to desynchronize the spot cycle of the first printhead and the spot cycle of the second printhead. Desynchronizing the spot cycles of the first printhead and the second printhead reduces the number of ejectors of the two printheads that are specified by the memory to be simultaneously actuated by the power supply.